The performance of the presently existing shielding gases for gas metal arc welding of austenitic stainless steels is normally optimized for specific situations such as welding positions and metal transfer modes. In welding shops, materials of a variety of thickness may be found and depending on the equipment or structure being manufactured, it is necessary to weld metals in different positions. The need for changing the shielding gas, according to material thickness, metal transfer mode and welding position dramatically affects the operation and therefore productivity in welding shops. Another important consideration is that every year, billions of dollars are spent worldwide in an effort to reduce and minimize corrosion problems and most of them are related to welded joints failures. International standards normally do not require any corrosion evaluation for the qualification of welding procedures for the 300 series austenitic stainless steels.
The mixtures currently available in the market had been developed by taking into consideration only specific objectives such as bead appearance, welding travel speed and mechanical properties. Besides that, the gas mixtures recommended for such materials do not perform equally in all modes of metal transfer, requiring very skilled welders or optimized arc welding equipment to ensure good results.
Various literatures have been provided in the field relating to shielding gas mixtures. Representative examples include: U.S. Pat. No. 5,739,503; N. Stenbacka et al., "Shielding Gases for GMAW of Stainless Steels", Scandinavian Journal of Metallurgy; Lyttle et al., "Select the Best Shielding Gas Blend for the Application", Welding Journal-November, 1990; W. Lucas, "Shielding Gases for Arc Welding-Part I", Welding and Metal Fabrication, June, 1992; and J. Medforth, "Shielding Gases for Stainless Steels", Australian Welding, second quarter, 1993, pp. 12-15. Nevertheless, none of the art, by itself or in any combination, is believed to lead to superior corrosion resistance and mechanical properties for welded joints and for superior stability.
It is therefore an object of the invention to develop a new gas mixture for the gas-metal arc welding of austenitic stainless steels that would enable higher productivity, enhance mechanical properties and corrosion resistance of welded joints.